Vader with eyebrows was a bit of a head scratch. I can only assume it’s an homage to OUROTJ.
Not sure: it’s only to use less than half a face that can be easily recognizable to Ahsoka. It helps to create the emotion of the scene. It you use the eyebrowless face, you don’t link CW Anakin to Rebels Anakin/Vader. That’s all.
I’m rewatching the entire series and I’m very surprised that the first season is in fact quite good (I’m half way through it, even the “Pitch Black” episode is a lot a fun - would be great to get Vin Diesel as an Inquisitor voice performer for season 3). Rebels really is a better series that Clone Wars: more character oriented, does play well with both OT and PT elements, best narrative value; whereas CW was essentially war porn and endless action scenes with minor (and uninteresting) movie characters. CW was only good when it was focused on Ahsoka and Anakin (and sometimes on Obi-Wan, Maul, Ventress); Rebels greatly benefits of it.
Let’s just hope they finish the series this time and don’t make it last beyond 3 or 4 seasons.
Just a thought: could Ezra be the “another one” Yoda mentions in ESB (since it’s not Leia, who has never managed to learn the ways of the Force) ? He’s the same age as Luke (both born on Empire Day). Or could he be related to the Knights of Ren ?